The present invention relates to the field of wireless data networks and systems and method for maintaining network service with mobile network clients. Wireless data networks allow computers or other electronic devices to exchange data without wires, typically using radio waves. Wireless networks are popular with users due to the ability to send and receive data almost anywhere within the physical coverage area of the network. This allows users to access communication networks, including local area networks, organization or company intranets, virtual private networks, and wide area networks, such as the Internet, anywhere within the physical coverage area of the wireless networks.
Wireless networks with large physical coverage areas, such as networks covering university campuses or entire cities, offer users ubiquitous access to their data and the Internet. However, typical wireless access points have ranges of around 100 feet. As a result, large wireless networks require tens, hundreds, or thousands of wireless access points to provide network coverage over a large physical area.
Configuring, managing, and operating a large number of wireless access points requires complicated network configurations. Typically, a large wireless network is divided into a number of different network subnets. Each network subnet includes one or more wireless access points. Each network subnet is assigned a specific range of IP addresses. All of the wireless access points within a subnet as well as the wireless client devices connected with these wireless access points are assigned IP addresses within the range of IP addresses associated with a subnet.
The use of multiple subnets within a wireless network introduces the problem of roaming. A wireless client, especially mobile devices, may move to different physical locations while connected with the wireless network. If a wireless client moves from the physical area associated with one wireless access point to a physical area associated with a second wireless access point, it is desirable for the wireless client to automatically connect with the second wireless access point to maintain its network connection. If both wireless access points are within the same subnet, the wireless client can keep the same IP address, allowing roaming to occur seamlessly without any noticeable disruption in the network connection or data traffic.
However, if a wireless client moves between wireless access points in different subnets, the wireless client cannot keep the same IP address. This is because each subnet has its own exclusive range of IP addresses. When the wireless client is connected with a wireless access point in a first subnet, the wireless client will have an IP address in the first subnet's IP address range. When the wireless client tries to connect with a wireless access point in a second subnet, its IP address is outside the second subnet's IP address range. As a result, the wireless client must be reauthenticated and assigned a new IP address that is valid for the second subnet. This process can cause noticeable disruption in the network connection and data traffic for the wireless client. This disruption is unacceptable for some applications, such as VOIP telephone applications.
The Mobile IP protocol is one approach for maintaining network connections of wireless devices. In the Mobile IP protocol, a wireless client is identified by its home address disregarding its current location in the Internet. The wireless client also carries the address of a home agent, which is a device located within the same subnet as its home address. When a wireless client moves from its home address to a new subnet, the wireless client locates a designated forwarding agent within the new subnet. The wireless client provides the forwarding agent with the address of its home agent. The forwarding agent then sets up a network tunnel with the home agent. Network traffic directed to the wireless client's home address is intercepted by the home agent and sent via the tunnel to the forwarding agent, which in turn forwards it to the wireless client. Similarly, network traffic from the wireless client is intercepted by the forwarding agent and sent via the tunnel to the home agent, which in turn forwards it to its intended destination.
One problem with the Mobile IP protocol is that it relies on the wireless client to maintain the network connection when roaming. The wireless client is responsible for carrying the address of the home agent and for contacting a forwarding agent as needed. To meet these responsibilities, the wireless client must either include a modified network driver stack or applications that support Mobile IP. The wireless client must keep track of two different IP addresses: the initial IP address in the client's “home” subnet and the IP address in the client's current subnet. Even if wireless clients include these capabilities, it is difficult and time-consuming to correctly configure large numbers of wireless clients to support Mobile IP roaming within a wireless network. Furthermore, wireless clients may need to be reconfigured whenever there are changes in network topology.
Therefore, there is an unmet need to enable wireless clients to roam without modifying the wireless client or its applications to support roaming protocols. There is also an unmet need for wireless clients to roam without requiring special configuration or knowledge of the network topology. There is also an unmet need to support wireless client roaming in an efficient and reliable manner.